Truck has CNG fuel alternative system but

[stillstrong170k]

but it will take a few hundred dollars to make the system complete as the CNG fuel tank is not, and has never been since owning, in the bed of the truck where it belongs. I bought the truck this way 3 years ago and hadn't given the idea of burning compressed natural gas much thought until now. So my question is, does anyone out there know or have the time to answer how a vehicle runs on compressed natural gas. Is it worth investing the extra money to complete the system considering mileage, power etc. which wouldn't be as good as regular gasoline? Truck is 1990 chevy cheyenne 1/2 ton 2wd with the 4.3L V6 if it makes any difference. Any help would be appreciated. Thanx.